On-Demand All-Wheel Drive Clutch Control for Torque Management
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Solution Overview
Problem
On-demand all-wheel drive systems without central and rear axle differentials experience torsional stresses, noise, vibrations, unwanted understeer, increased tire wear, and fuel consumption due to lack of speed synchronization and torque imbalance between front and rear wheels during turns.
Innovation Solution
A method that determines which rear wheel is outer when bending and disengages the partial clutch assigned to it if there's negative torque, using speed synchronization between front wheels to assess torque conditions and adjust clutch engagement dynamically to prevent understeer and reduce traction loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If both partial clutches are engaged in on-demand all-wheel drive systems, then driving power is transmitted to all wheels, but torsional stresses occur in the drivetrain at low speed and with lateral acceleration causing noise and vibrations
Solution Approach 1:
The patent applies dynamics by continuously monitoring wheel speeds and dynamically adjusting clutch engagement based on real-time driving conditions. The control unit engages or disengages partial clutches depending on whether speed synchronization is achieved, allowing the system to adapt between two-wheel drive and four-wheel drive modes to avoid torsional stresses and noise while maintaining power transmission when needed.
Solution Approach 2:
The patent changes the operational parameters of the clutch system by using speed synchronization as a control parameter. When the speed difference between front and rear wheels exceeds a threshold, the system changes the clutch engagement state to prevent torsional stresses. This parameter-based control resolves the contradiction by adjusting power transmission based on actual speed conditions.
2Power
If both partial clutches are engaged without speed synchronization, then all wheels receive drive power, but unwanted understeer occurs on tight bends due to negative torque on the outer rear wheel
Solution Approach 1:
The patent implements feedback control by continuously monitoring wheel speeds and using this information to control clutch engagement. The control unit receives feedback on the speed difference between front and rear wheels and adjusts the partial clutch state accordingly. This feedback mechanism prevents negative torque conditions that cause understeer by disengaging the outer rear clutch when speed synchronization is not achieved.
Solution Approach 2:
The system dynamically adjusts clutch engagement based on real-time speed measurements and driving conditions. By continuously adapting the drivetrain configuration to current operational parameters, the system prevents understeer on tight bends while maintaining power transmission capability when speed synchronization is achieved.
3Power
If both partial clutches are engaged without speed synchronization, then four-wheel drive is activated, but greater tire wear occurs due to tire scrubbing
Solution Approach 1:
The patent uses speed synchronization as a control parameter to determine clutch engagement state. When the speed difference between axles exceeds a threshold, the system changes the drivetrain configuration from four-wheel drive to two-wheel drive, preventing tire scrubbing and excessive wear while maintaining power transmission when synchronization is achieved.
4Power
If both partial clutches are engaged without speed synchronization, then all wheels are driven, but increased fuel consumption occurs due to negative torques
Solution Approach 1:
The patent extracts the unnecessary power transmission path by disengaging the partial clutch on the outer rear wheel when speed synchronization is not achieved. This eliminates the negative torque and associated energy loss, reducing fuel consumption while maintaining power transmission capability when needed. The system takes out the problematic drivetrain connection rather than attempting to correct it.
Data Source
AI summary
A vehicle includes a powerplant, a front axle having first and second wheels and a differential operably coupled to the powerplant. A power-takeoff unit (PTU) is connected to the differential. A rear axle has third and fourth wheels and a gearbox connected to the PTU without a center differential. The gearbox has a first clutch configured to selectively couple the third wheel to the PTU and a second clutch configured to selectively couple the fourth wheel to the PTU. A controller is programmed to determine, during a turn, which of the third and fourth wheels is an outer rear wheel, determine whether there is a positive or negative torque on the outer rear wheel, and disengage, or keep disengaged, the one of the first and second clutches that is associated with the outer rear wheel in response to a negative torque on the outer rear wheel.